Nucleotide sequence analysis of the rubella virus genomic RNA revealed that there is a 12bp inverted repeat located at the 3'end of the RNA, that is capable of forming a stem-loop structure. This inverted repeat is present in the region of the RNA which is implicated to be involved in the replication of the virus. Specific high-affinity binding of three cytosolic phosphoproteins with the stem-loop structure has been observed. The binding of the host proteins is greatly increased after infection and coincides with the appearance of negative strain RNA synthesis. In order to analyse the function of this cis-acting element in the replication or transcriptional process, experiments were performed where an 158bp sequence containing the stem-loop structure was isolated and tested for its promoter activity in a series of CAT (Chloramphenicol Acetyltransferase) expression vectors. The recombinant plasmids were transfected into cos-1 cells. The results showed that only the vector containing the 158bp fragment in 5'-3' orientation with the CAT gene has promoter activity and it is dependent upon the SV40 enhancer element present in the vector. Deletion experiments of the promoter are in progress to pinpoint the region which is necessary for the promoter function. Using 158bp fragment as a probe, we are looking for a region in the host cell genome which is complementary to this sequence and can potentially function as a promoter. In addition, the role of SV40 T antigen, if any, is being tested also in the promoter activity.